1. Field of the Invention
The present invention relates to an electron gun and, more particularly, to an electron gun for creating a high-intensity electron beam.
2. Description of the Prior Art
The utility of a high-intensity, fine-line electron beam in various processes is discussed in U.S. Pat. No. 4,382,186 (which has been disclaimed in favor of application Ser. No. 455,266, now U.S. Pat. No. 4,446,373, which is assigned to the assignee of the present invention). Such an electron beam can be used, as disclosed therein, for fabricating semiconductor devices and generally modifying the surface of materials in various advantageous ways.
One such operation that has great potential commercial significance is the formation of a large single crystal from a layer of amorphous silicon on a substrate. The amorphous silicon is melted using a strip electron beam and then recrystalized into a single crystal. That is disclosed in U.S. Pat. Nos. 4,382,186 and 4,446,373. However, that operation cannot be optimally performed with existing electron beam guns.
The "power density" or "flux" of the electron beam has been found to be a critical parameter in enabling the formation of a single silicon crystal from an amorphous layer of polysilicon. The power density of the beam is the wattage per unit area to which the beam target is subjected. If an electron beam comprises a given number of electrons each having a particular kinetic energy as it reaches the target, the power density in megawatts (MW) per square centimeter (cm.sup.2) is increased as the beam area is reduced.
Presently known electron guns capable of producing a fine-line electron beam can provide power densities in the range up to 0.2 MW/cm.sup.2. However, that power density, while adequate for production of large, single-crystal semiconductor devices of recrystallization of an amorphous layer that was melted using the electron beam, is too low for optimal efficiency.